1. Field
This disclosure relates generally to integrated circuit memory, and more specifically, to a memory having a latching sense amplifier resistant to negative bias temperature instability (NBTI) and method therefor.
2. Related Art
A one-time programmable (OTP) memory is a type of memory that is used to permanently store programs or data in integrated circuit applications. An OTP memory cell may be implemented using, for example, fuses or antif uses. Read disturb can occur in an OTP memory cell as a result of read current being repeatedly applied to the OTP memory cell, such as an electrically programmable fuse or antif use, and thus causing a stress condition in the OTP memory cell. Repeated read current stress can progressively alter the logic state of an OTP memory cell, and after a long time period move the cell from an unprogrammed state to a programmed state, causing an error. It is therefore desirable to read the OTP memory cell as little as possible. One way to avoid reading the OTP memory cell is to use a read operation to store the logic state of the OTP memory cell in a latching sense amplifier. For example, OTP memory cells may be used in a parallel block architecture where each OTP memory cell is coupled to a latching sense amplifier. The latching sense amplifiers can then be read in parallel. The sense amplifiers may include cross-coupled latches implemented using complementary metal oxide semiconductor (CMOS) process technology. If the system requires the logic state of the OTP memory cell, it can acquire the logic state from the latching sense amplifier without disturbing the OTP memory cell. This operation is called a “soft read”. Only after an event, such as for example, a system on-off-on power cycle, another read operation has to be performed that actually reads from the OTP memory cell. This operation is commonly referred to as a “hard read”. However, because the same data is always latched in the sense amplifiers, a threshold voltage (VTH) shift of PMOS (p-type metal oxide semiconductor) transistors in the sense amplifier latches can occur because of negative bias temperature instability (NBTI). NBTI drift results in a sense amplifier offset increasing over time and may result in incorrect sensing over a long time period.
Therefore, what is needed is a latching sense amplifier that solves the above problems.